Influence of the martensitic transformation on the hydrogenation properties of Ti50-xZrxNi50 alloys

Ti50-xZrxNi50 alloys with 0less than or equal toxless than or equal to24 develop either austenitic or martensitic crystal structures when prepared by melt-spinning or induction melting, respectively. This outcome is a consequence of the particular alloy microstructure resulting from each preparation method, which induces a difference of 100degreesC on the martensitic transformation temperatures for alloys with the same composition. Austenitic alloys absorb hydrogen up to 1.5 hydrogen atoms per AB unit (H/AB) at 130degreesC and 20 bar, without displaying any plateau pressure for hydrogen pressures between 0.1 and 10 bar. In contrast, martensitic alloys exhibit a plateau pressure with hydrogen concentrations between I and 2.1 H/AB, and reach a maximum hydrogen concentration of 2.6 H/AB under the same thermodynamic conditions. Consequently, martensitic alloys form a dihydride compound that, for the representative case of Ti32Zr18Ni50 alloy, has a formation enthalpy of -12.3 +/- 0.2 kcal mol H-2(-1). (C) 2002 Elsevier Science B.V. All rights reserved.